Method of machining composites

ABSTRACT

There is now provided a method of machining and shaping a through opening in a fiber-reinforced composite material starting from a preformed hole. At least one rotation symmetrical milling body with a substantially smaller diameter than that of the preformed hole is placed in that hole and the opening is machined and shaped by the milling body partly rotating around its own axis, partly by a translational movement relative to the edge of the opening. According to the method, the fiber-reinforced material is oriented in such a way that the axis of rotation of the milling body is essentially perpendicular to the longitudinal direction of the fibers at the edge of the opening. The size and/or form of the finished opening differs significantly from that of the preformed hole. The radial spread of the damages and/or the defects define a lower limit for the amount of material removed.

This application is a continuation of application Ser. No. 08/428,702,filed Apr. 25, 1995, abandoned, a continuation of application Ser. No.08/063,696, filed May 20, 1993, abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of machining and shaping athrough opening in a fiber-reinforced composite material.

Swedish patent application 9201420-8 discloses a method of machining andshaping a through opening with damage-free edges in a fiber-reinforcedcomposite material with high precision by placing a rotationallysymmetrical grinding body in a preformed hole with the compositematerial being oriented in such a way that the axis of rotation of thegrinding body is essentially perpendicular to the longitudinal directionof the fibers at the edge of the opening. The opening is machined andshaped by the grinding body partly rotating around its own axis, partlyperforming a revolving motion relatively to the edge of the opening.Grinding, however, is a slow process with several limitations to itseffective commercial use in such a method.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to avoid or alleviate the problems ofthe prior art.

It is further an object of this invention to provide an improved methodof machining and shaping a through opening in a fiber-reinforcedcomposite material.

The present invention provides a method of machining and shaping athrough opening in a fiber-reinforced composite material starting from apreformed hole comprising placing at least one rotationally symmetricalmilling body with substantially smaller diameter than that of thepreformed hole in said hole and machining and shaping the desiredopening with the milling body partly rotating around its own axis andpartly by performing a translational movement relative to the edge ofthe opening, the fiber-reinforced material in the composite beingoriented so that the axis of rotation of the milling body is essentiallyperpendicular to the longitudinal direction of the fibers at the edge ofthe opening, the size and/or geometry of the finished opening differingsignificantly from that of the preformed hole, the radial spread of thedamages/defects arising from the preforming of said hole defining alower limit for the amount of material removed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described closer in the following under reference tothe accompanying drawings in which one embodiment is shown by way ofexample. This embodiment can however be modified within the scope of theclaims.

FIGS. 1A, 1B, 2A and 2B illustrate how a through opening is shaped in afiber-reinforced composite plate using a rotationally symmetricalmilling cutter body according to the present invention.

In FIGS. 1A, 1B, 2A and 2B, 1 is the fiber-reinforced laminate, 2 is thepreformed hole, 3 is the milling body, 5 is the axis of rotation of themilling body, and 6 is the damages and/or defects. In FIG. 2A, 7 is thefinished opening.

FIG. 3 shows a side view of a milling cutter provided with insertsuseful in the present invention.

FIG. 4 shows a top view of the mill in FIG. 3.

In FIGS. 3 and 4, 10 is the milling body, 11 is an insert, 12 is thecentral hole in an insert 11, 13 is the side surface of an insert 11, 14is the clearance face of an insert 11, and 15 is the edge surface of aninsert 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

It has now turned out that by using a milling body rather than agrinding tool, a significantly higher rate of cutting, less heatgeneration as well as better machining economy can be obtained.

According to the present invention, there is now provided an improvedmethod of machining and shaping a through opening in a fiber-reinforcedcomposite material. The method is described for the case as shown inFIGS. 1A, 1B, 2A and 2B where the material is present in form of a planeplate 1, a laminate composed of a number of lamellas containingcontinuous fiber reinforcements, whereby the lamellas are piled on topof each other. The fibers lie oriented in planes parallel to the planeof the laminate, whereby the fiber directions are 0°, 90°, 45° and -45°.An opening 2 in the laminate is shaped first by, for example, drilling.Damages and/or other defects 6 frequently arise at the edge of theopening. In the preformed hole 2, a rotationally symmetrical millingbody 3 having spiral cutting edges 3A is placed. A distance D betweenopposite ends of each cutting edge 3A in a direction parallel to theaxis of rotation is greater than a depth d of the hole 2. Also, eachcutting edge extends around the axis less than 360 degrees within thehole. That is, the portion of each cutting edge extending within thedepth d of the hole 2 extends circumferentially for less than 360degrees, as can be seen in FIG. 1B for example. The laminate is orientedin such a way that the axis of rotation of the milling body 5 isperpendicular to the longitudinal direction of the fibers in the plate1, i.e., perpendicular to the plane of the laminate. The opening 2 ismachined by the milling body 3 partly rotating around its own axis 5 andpartly by performing a translational movement relative to the edge ofthe opening 2 so that the damage and other defects 6 resulting from theshaping of the opening 2 are removed. The size and/or form of thefinished opening 7 differs substantially from that of the preformed hole2. While the finished opening can have any desired shape and size,machining with the milling body is conducted to at least remove thedamage or other defects 6.

The milling body is suitably a so-called long edge milling cutter ofhigh speed steel or solid cemented carbide or a metal-base with brazedor indexable, removable inserts of cemented carbide, titanium-basedcarbonitride alloy (so-called cermet) or ceramics. Such inserts arewell-known in the art and inserts of these types can be used. Themilling cutter (if high speed steel or cemented carbide) or the insertsare preferably coated with at least one thin layer of wear resistantmaterial such as TiC, TiN and/or Al₂ O₃ applied by the known CVD- andPVD-methods as known in the art. A thin layer of diamond is aparticularly suitable coating. The total thickness of the coated layeris 20 μm, preferably 2-10 μm.

Alternatively, the milling cutter contains one or more diamond bodies orsaid inserts are diamond impregnated, e.g., according to U.S. patentapplication Ser. No. 07/811,527, incorporated herein by reference.

Particularly appropriate for use in the process of the present inventionis the so-called drilling mill whereby the whole operation can beperformed with only one tool.

For making larger openings, a milling cutter with the design shown inFIGS. 3 and 4 is particularly suitable. This milling cutter is a millingbody 10 equipped with removable inserts 11. The inserts 11 can beprovided with a central hole 12 through the insert, wherein a threadedlocking pin (not shown) is inserted to clamp the insert 11. Whenmachining, the milling cutter rotates counterclockwise in FIG. 4 wherebythe side surface 13 of the insert 11 forms the clearance face of thecutting edge 14 and the edge surface 15 forms the edge of the insertchip face. A number of inserts 11 in the shown embodiment are arrangedin a spiral path in the longitudinal direction of the milling body 10.Four such spiral paths are uniformly distributed around thecircumference of the milling body 10.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A method of machining and shaping a preformedinitial hole in a fiber-reinforced composite, an edge of said initialhole having damages or defects possessing a radial spread, said methodcomprising the steps of:A) placing in said initial hole a machining toolhaving a smaller diameter than said initial hole, said tool including abody defining a longitudinal axis of rotation, and a plurality ofcutting edges disposed symmetrically on an outer periphery of said body,and extending generally spirally about said axis of rotation, a distancebetween opposite ends of each spiral cutting edge in a directionparallel to said axis of rotation being greater than the depth of saidinitial hole, each of said cutting edges extending continuously betweensaid ends thereof and around said axis of rotation less than 360 degreeswithin said initial hole, said axis of rotation oriented substantiallyperpendicular to a longitudinal direction of reinforcement fibersdisposed at said edge; B) moving said body along said edge of saidinitial hole while rotating said body about said axis of rotation andwhile maintaining said ends of said spiral cutting edges outside of saidinitial hole, with said axis of rotation offset radially from a centeraxis of said initial hole and with said cutting edges in contact withsaid edge of said initial hole so as to enlarge said initial hole into afinished opening; C) performing step B to remove an amount of saidcomposite wherein a lower limit of said removed amount is defined bysaid radial spread of said damages or defects; and D) removing themachining tool from the enlarged hole.
 2. The method according to claim1 wherein each of the cutting edges is defined by a plurality of spacedapart cutting inserts arranged in a generally spiral path.
 3. The methodaccording to claim 2 wherein the inserts are formed of cemented carbide.4. The method according to claim 2 wherein the inserts are formed of aceramic.
 5. The method according to claim 2 wherein the inserts arecoated with diamond.
 6. The method according to claim 2 wherein theinserts are indexable.